This invention relates to gate valves and more particularly to fluid-operated gate valves including automatic interlock means for preventing closure due to loss of fluid supply pressure, or operational error.
Gate valves are used extensively in vacuum applications because of their short unrestricted flow path and larger available orifice or throat sizes. They are used as gating and isolation means for vacuum pumps and system components, access means or ports and interconnecting penetrations between apparatus.
In these latter two applications, analytical equipment or probes may be inserted through the gate valve throat while at vacuum pressures. Upon removal for repair or alteration the gate valve is then closed to maintain apparatus vacuum integrity.
A vacuum exerts a force on the valve gate, unlike high pressure applications, pulling the gate into the valve throat from its out of throat, open, position. Fluid pressure against the gate actuator keeps the valve fully open in fluid operated gate valves. Therefore, loss of fluid pressure with the gate under vacuum conditions allows the valve to creep closed. The extent of the gate valve closure depends on the operating parameters of the specific gate and vacuum apparatus. It is clear that if equipment or materials are present in the valve throat, premature closure can damage the gate, equipment or materials from sudden contact or from subsequent attempts at movement, such as when automatic insertion/removal means are activated. Additionally, any vacuum pump gated by a prematurely closing gate valve loses pumping capacity thereby allowing increased pressures in the vacuum apparatus with potentially deleterious effects. These same results occur in cases of operational error, when through error premature valve closure is instigated by operating personnel.
Existing gate valve locking devices fail to adequately protect valves and apparatus inserted therein, in high vacuum applications, because they are typically designed for locking a gate valve closed against high pressure, such as in U.S. Pat. No. 3,695,578 dated Oct. 3, 1972 issued to Walther, et. al., where locking a gate valve open under pressure conditions was stated as unnecessary.
Advanced valves with multiple gates and complex sealing means make mechanical locking devices that interact with the gate, such as in U.S. Pat. No. 3,523,675 dated Aug. 11, 1970 issued to M. H. Grove, et. al., more complex and impractical. Pressure actuated locking devices also require greater forces to disengage, when used on an evacuated gate housing, increasing hardware stress and risk of pressure intrusion into the vacuum.
Plasma confinement devices and reactors can use 100 or more gate valves with associated probes or equipment. In this environment, using locking devices that have pressure input sources separate from the valve actuating source; means for detecting the pressure level of the pressure input sources; or check valves in the pressure input lines, creates complexity that increases the likelihood of pressure loss. Locking devices utilizing pressure control valves for activating the lock also increase the amount of personnel interaction necessary, increasing the risk of operational error.
Adequate interlock capability for prevention of operational errors on vacuum systems with a large number of gate valves requires both automatic operation and a direct interaction with pressure actuators for other apparatus. A pressure control means functioning as an integral part of a locking device would provide this automatic operation with reduced complexity or need for human intervention.
It is also clear that many gate valves of proven reliability exist and there is no need to totally redesign an entire valve to achieve a reliable locking function. A simple, small scale, inexpensive valve add on or improvement is needed which minimizes changes in size or operating characteristics, allowing ready implementation on a variety of vacuum apparatus gate valves.